The present invention relates to a method and an apparatus for measuring the intensity of radiation from a radiation source and, in particular, to a method and apparatus for measuring the intensity of light from each of the segments of a multi-segmented light-emitting device. A representative example of devices of this type is a light-emitting diode. Diodes of the type described are used, for example, in electronic watches, instrumentation and the like.
In the manufacture of LED's as light-emitting diodes and similar devices are conveniently called, the intensity of the radiation from the devices is measured. If a device is a multi-segmented device with means for providing radiation from each of the segments, then frequently it is desired to test all the segments for a uniform intensity of radiation.
Presently, general area-wide illumination in most testing facilities is by means of incandescent radiation, fluoroscent radiation, or both. To test the intensity of radiation from an LED, it has been necessary to perform the task in a darkroom, in a radiation-shielded area which is shielded from the incandescent and fluorescent radiation, or, if testing is done in the presence of ambient radiation, to compensate for the ambient radiation in some manner.
Both incandescent and fluorescent fixtures are generally operated using 60 Hz power. Using 60 Hz power, there is in the radiation a d.c. component as well as a periodic component having a frequency or repetition rate of 120 Hz.
Considering the radiation from both types of light sources, an incandescent lamp using a filament is considerably less responsive to the cyclical nature of the supply power than is a fluorescent lamp. Because of this, the radiation from an incandescent lamp is frequently considered and treated as d.c. or constant, whereas the radiation from a fluorescent lamp includes a significant 120 Hz component.
Heretofore, the testing of the intensity of radiation from a source of optical radiation in the presence of ambient radiation has been performed in the presence of incandescent radiation by ignoring the small perturbation due to the 60 Hz power. To avoid the necessity of providing for special lighting, it is desirable to be able to test devices in fluorescent, as well as incandescent ambient radiation.